It is well known that architects in the United States continue to use English systems of measurements in architectural drawings, despite the popularity of the metric system in other parts of the world and its ease of use. Consequently, most carpenters and builders executing the plans of architects also use the English system of measurements involving feet and inches. Traditionally, the resolutions of dimensions for architects, carpenters and others in the building trade have been expressed in proper fractions of inches with denominators which are integer powers of two.
Since inches to feet is a base twelve system, our normal numbering system is a base ten system, and the denominators of the proper fractions used are integer powers of two (which excludes ten and twelve as possibilities), simple arithmetic operations on the English system of measurements is somewhat cumbersome. It is not unlike trying to do arithmetic in Roman numerals.
When a reasonably large number of arithmetic calculations are required in the English system, people often convert each individual term of an expression to its decimal foot equivalent and reconvert the result to English measurements. When using hand-held calculators, such a conversion requires a relatively large number of keystrokes, and it is often difficult for the user to remember exactly what register or position in a stack in which the various values are stored.
To overcome this, dedicated calculators making provisions for entry of data representative of inch and feet quantities have been known in the past. The principal drawback of such devices is the absence of an ability to switch back and forth between operating modes without accumulated round-off error, an absence of functions and display modes particularly useful to the architect or builder. Other prior art calculators employ cumbersome direct accumulation of digits representing fractions, feet, and index, with somewhat exotic schemes for converting results of addition of integer values for numbers in various bases in order to convert from, for example, sixteenths of an inch to inches (base sixteen), and inches to feet (base twelve).
In the building trades, many materials are provided in sections having a standard length. Often the builder encounters a situation in which a number of pieces of a particular material of identical length are required for a job. Therefore, the builder needs to know how many such pieces can be obtained from a piece of the material supplied in the standard length. In essence, the user needs to know only the integer result of dividing the standard length by the unit length of the individual pieces to be cut. Once this is obtained, the total number of standard pieces needed for the job may quickly be derived.
In most of these situations, the user will have very little interest in the length of the remainder.
In other situations, the builder may need to divide a particular length expressed in feet, inches, and fractions of inches into an even number of equal segments. One example of such an application would be the building of a cabinet or shelf on the center third of a wall. Under these circumstances, the builder would need to divide the length of the wall, a quantity dimensioned in English units, by an undimensioned integer 3. The result is 1/3 of the length of the wall, and gives the user an indication of how far from each end of the wall the shelf should be placed, as well a figure for the length of the shelf.
It should be noted that in the first case, the information desired is the result of dividing one dimensioned quantity by another, giving an unsigned result indicating the number of the smaller pieces which may be cut from the standard piece. In the second example, the operation is the division of a dimensioned quantity by an undimensioned quantity to provide a dimensioned result.
It is also known in the art of designing dedicated calculators to provide calculators designed to be used in English units which will automatically convert an English unit quantity to a metric quantity, normally in meters. However, such calculators have normally replaced values for English units with metric values resulting from a multiplication. Repeated conversions, back and forth, of this type can lead to accumulated round off error.
Additionally, architects and practitioners of the building trades often encounter repeated occurrences of a particular dimension when working. For example, if one is attempting to calculate the total length of a portion of office space from a set of plans, the user will often encounter an object of a standard dimension, such as an eight inch wall. When moving along the plans and using a calculator, it can become cumbersome to continually have to execute key strokes corresponding to "plus eight inches". Under these circumstances, it is often desirable to be able to add dimensions of the other elements of the plan and then come back and do an appropriate operation for each wall.
Furthermore, in a number of plans, there will be several recurring dimension.
Prior art calculators have not provided a straightforward and convenient mechanism for easing use of a dedicated English unit calculator under these circumstances.
Additionally, dedicated English system calculators of the type which maintain separate integer values for feet, inches and fractions of a particular denominator, have not provided the ability to multiply decimal fractions of inches, which for example, are not equivalent to a proper fraction of sixteenths of inches, and to display the result with acceptable accuracy. Indeed, many such prior art calculators have a lowest resolution of a number which may be accepted by the calculator as the smallest proper fraction handled, such as 1/16th or 1/32nd of an inch.
Therefore, there is a need in the art of dedicated English unit calculators to provide a device which overcomes these shortcomings and has a great flexibility in the operations which may be performed without sacrificing accuracy. Additionally, it is desirable to provide a calculator which will display an undimensioned integer quantity in response to a keystroke sequence requesting the quotient of two quantities in English units and optionally to provide the user with a remainder expressed in English units. Furthermore, it is desirable to provide a calculator in which the user may also divide a dimensioned English unit quantity by a numerical value representing an undimensioned quantity and display a result in English measurements.
Similarly, the prior art has not provided an English unit calculator which provides simpler keystroke operations for recursive entry of an identical operation, particularly the addition of one or more repeatedly encountered quantities to an accumulated sum.